Thanks! Description will be improved over time.^^
I added an image at the very top for a better overview. The generator basically just generates text as outpout, doing it for each found table entry. But by default for example, if I open a map's terrain file with this tool, and press "Generate all", then it would give me ready to use JASS code to create the entire map terrain. It just loops over all found terrain tiles from table and creates the respective SetTerrainType function call. Like in the screenshot. I can now take this code and put it some other map to re-create it there. Usually it makes sense to limit the generation to a certain x/y min/max bounds, etc.
There are just small test examples without much sense on my comp, but I try to post a concrete one soon.
A friend wanted to have for example the cities in his map to have different terrain styles, winter/summer, and he wanted to change it dynamically in game. And doing such terrain changes manually and with fixed coordinates can be a bit awful. So he wanted just to take a "rect" out of the map, and have the terrain stored in code automatically.